1. Field of the Invention
The invention relates to an adjustable vibration damper.
2. Discussion of the Prior Art
In adjustable vibration dampers which are used together with pneumatic springs, there is an increasing tendency to utilize the pressure in the pneumatic spring of the vehicle as a control signal for an adjustable damping valve on or in the vibration damper. The essential advantage of these damping valves controllable by air pressure is the simple and therefore also cost-effective design. Particularly in the commercial vehicle sector, the aim is to achieve simple and robust solutions, since the chassis components are exposed to very high loads on off-highway journeys.
Due to the high loads, pneumatic springs may become leaky because of the embrittlement of the pneumatic spring bellows. It must also be taken into account that a pneumatic spring may burst. For the activation of the pneumatic spring, there is the important difference as to whether a low control pressure is present because of a low vehicle load or because of a leak.
For this type of pneumatic spring failure, German reference DE 41 05 771 A1 discloses a solution in which a pneumatic control pressure is used for an adjustable damping valve. A relatively complicated damping valve is employed, in which a control piston is subjected on one side to a control pressure and on the other side to a reference pressure. The atmosphere serves as reference pressure. As soon as the control pressure falls short of a particular level, the reference pressure presses the control piston into an operating position which is linked to a higher damping force for the vibration damper.
The object of the present invention is to provide an adjustable vibration damper which, when the control pressure fails, can continue to build up a sufficient damping force.
The object is achieved, according to the invention, in that at least two pneumatic springs are connected to the safety device, which is constructed from a pneumatic circuit functioning as a pressure balance between the pneumatic springs which releases the higher control pressure of a pneumatic spring in the pneumatic circuit. The adjustable vibration dampers which belong to the pneumatic springs are connected via at least one pressure outlet connection of the pneumatic circuit and are activated by means of the higher control pressure of the pneumatic springs involved.
The pneumatic circuit represents an interrogation device. It is assumed that the higher control pressure is, under all circumstances, on the safe side of the operation of the pneumatic spring. An intact system can always generate a higher pressure than a defective pneumatic spring. The faulty control pressure is consequently filtered out.
The simplest variant is distinguished in that the pneumatic circuit consists of a shuttle valve which has connections to the pneumatic springs. A shuttle valve known per se may be used. This affords the advantage that two pneumatic springs are protected by means of one shuttle valve.
There may be provision for using the vibration damper in a vehicle axle, the pneumatic springs of a vehicle axle being connected to the pneumatic circuit. This design makes it possible, within limits, to have a beneficial influence on the rolling behavior of a vehicle since all the vibration dampers of a vehicle axle are activated by means of the higher control pressure of the pneumatic spring on the outside of a bend.
Alternatively, the vibration damper may be used in a vehicle having a plurality of pneumatically suspended axles, the pneumatic springs of different axles being connected to the pneumatic circuit. The background to this is the philosophy that one pneumatic spring has burst because of an excessive axle load. The remaining pneumatic spring is consequently subjected to even higher load on this axle, so that the probability of further failure increases. If, however, the control pressure of a pneumatic spring of another axle is used, the adjustable valve of the vibration damper can continue to be operated with a greater degree of safety.
There is also the possibility of using the vibration damper in a vehicle having a plurality of pneumatically suspended axles, the pneumatic springs of a number of axles being connected, in each case per axle, and the pneumatic springs of different axles being connected to the pneumatic circuit. In this case, the pneumatic springs are always compared with one another in pairs and the pneumatic spring released at the time is compared with another released pneumatic spring.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention